//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file defines the primary stateless implementation of the // Alias Analysis interface that implements identities (two different // globals cannot alias, etc), but does no stateful analysis. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/Passes.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallVector.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/CFG.h" #include "llvm/Analysis/CaptureTracking.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/GetElementPtrTypeIterator.h" #include "llvm/IR/GlobalAlias.h" #include "llvm/IR/GlobalVariable.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Operator.h" #include "llvm/Pass.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Target/TargetLibraryInfo.h" #include using namespace llvm; /// Cutoff after which to stop analysing a set of phi nodes potentially involved /// in a cycle. Because we are analysing 'through' phi nodes we need to be /// careful with value equivalence. We use reachability to make sure a value /// cannot be involved in a cycle. const unsigned MaxNumPhiBBsValueReachabilityCheck = 20; // The max limit of the search depth in DecomposeGEPExpression() and // GetUnderlyingObject(), both functions need to use the same search // depth otherwise the algorithm in aliasGEP will assert. static const unsigned MaxLookupSearchDepth = 6; //===----------------------------------------------------------------------===// // Useful predicates //===----------------------------------------------------------------------===// /// isNonEscapingLocalObject - Return true if the pointer is to a function-local /// object that never escapes from the function. static bool isNonEscapingLocalObject(const Value *V) { // If this is a local allocation, check to see if it escapes. if (isa(V) || isNoAliasCall(V)) // Set StoreCaptures to True so that we can assume in our callers that the // pointer is not the result of a load instruction. Currently // PointerMayBeCaptured doesn't have any special analysis for the // StoreCaptures=false case; if it did, our callers could be refined to be // more precise. return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); // If this is an argument that corresponds to a byval or noalias argument, // then it has not escaped before entering the function. Check if it escapes // inside the function. if (const Argument *A = dyn_cast(V)) if (A->hasByValAttr() || A->hasNoAliasAttr()) // Note even if the argument is marked nocapture we still need to check // for copies made inside the function. The nocapture attribute only // specifies that there are no copies made that outlive the function. return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); return false; } /// isEscapeSource - Return true if the pointer is one which would have /// been considered an escape by isNonEscapingLocalObject. static bool isEscapeSource(const Value *V) { if (isa(V) || isa(V) || isa(V)) return true; // The load case works because isNonEscapingLocalObject considers all // stores to be escapes (it passes true for the StoreCaptures argument // to PointerMayBeCaptured). if (isa(V)) return true; return false; } /// getObjectSize - Return the size of the object specified by V, or /// UnknownSize if unknown. static uint64_t getObjectSize(const Value *V, const DataLayout &DL, const TargetLibraryInfo &TLI, bool RoundToAlign = false) { uint64_t Size; if (getObjectSize(V, Size, &DL, &TLI, RoundToAlign)) return Size; return AliasAnalysis::UnknownSize; } /// isObjectSmallerThan - Return true if we can prove that the object specified /// by V is smaller than Size. static bool isObjectSmallerThan(const Value *V, uint64_t Size, const DataLayout &DL, const TargetLibraryInfo &TLI) { // Note that the meanings of the "object" are slightly different in the // following contexts: // c1: llvm::getObjectSize() // c2: llvm.objectsize() intrinsic // c3: isObjectSmallerThan() // c1 and c2 share the same meaning; however, the meaning of "object" in c3 // refers to the "entire object". // // Consider this example: // char *p = (char*)malloc(100) // char *q = p+80; // // In the context of c1 and c2, the "object" pointed by q refers to the // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20. // // However, in the context of c3, the "object" refers to the chunk of memory // being allocated. So, the "object" has 100 bytes, and q points to the middle // the "object". In case q is passed to isObjectSmallerThan() as the 1st // parameter, before the llvm::getObjectSize() is called to get the size of // entire object, we should: // - either rewind the pointer q to the base-address of the object in // question (in this case rewind to p), or // - just give up. It is up to caller to make sure the pointer is pointing // to the base address the object. // // We go for 2nd option for simplicity. if (!isIdentifiedObject(V)) return false; // This function needs to use the aligned object size because we allow // reads a bit past the end given sufficient alignment. uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/true); return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size; } /// isObjectSize - Return true if we can prove that the object specified /// by V has size Size. static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL, const TargetLibraryInfo &TLI) { uint64_t ObjectSize = getObjectSize(V, DL, TLI); return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size; } /// isIdentifiedFunctionLocal - Return true if V is umabigously identified /// at the function-level. Different IdentifiedFunctionLocals can't alias. /// Further, an IdentifiedFunctionLocal can not alias with any function /// arguments other than itself, which is not necessarily true for /// IdentifiedObjects. static bool isIdentifiedFunctionLocal(const Value *V) { return isa(V) || isNoAliasCall(V) || isNoAliasArgument(V); } //===----------------------------------------------------------------------===// // GetElementPtr Instruction Decomposition and Analysis //===----------------------------------------------------------------------===// namespace { enum ExtensionKind { EK_NotExtended, EK_SignExt, EK_ZeroExt }; struct VariableGEPIndex { const Value *V; ExtensionKind Extension; int64_t Scale; bool operator==(const VariableGEPIndex &Other) const { return V == Other.V && Extension == Other.Extension && Scale == Other.Scale; } bool operator!=(const VariableGEPIndex &Other) const { return !operator==(Other); } }; } /// GetLinearExpression - Analyze the specified value as a linear expression: /// "A*V + B", where A and B are constant integers. Return the scale and offset /// values as APInts and return V as a Value*, and return whether we looked /// through any sign or zero extends. The incoming Value is known to have /// IntegerType and it may already be sign or zero extended. /// /// Note that this looks through extends, so the high bits may not be /// represented in the result. static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, ExtensionKind &Extension, const DataLayout &DL, unsigned Depth) { assert(V->getType()->isIntegerTy() && "Not an integer value"); // Limit our recursion depth. if (Depth == 6) { Scale = 1; Offset = 0; return V; } if (BinaryOperator *BOp = dyn_cast(V)) { if (ConstantInt *RHSC = dyn_cast(BOp->getOperand(1))) { switch (BOp->getOpcode()) { default: break; case Instruction::Or: // X|C == X+C if all the bits in C are unset in X. Otherwise we can't // analyze it. if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &DL)) break; // FALL THROUGH. case Instruction::Add: V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, DL, Depth+1); Offset += RHSC->getValue(); return V; case Instruction::Mul: V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, DL, Depth+1); Offset *= RHSC->getValue(); Scale *= RHSC->getValue(); return V; case Instruction::Shl: V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, DL, Depth+1); Offset <<= RHSC->getValue().getLimitedValue(); Scale <<= RHSC->getValue().getLimitedValue(); return V; } } } // Since GEP indices are sign extended anyway, we don't care about the high // bits of a sign or zero extended value - just scales and offsets. The // extensions have to be consistent though. if ((isa(V) && Extension != EK_ZeroExt) || (isa(V) && Extension != EK_SignExt)) { Value *CastOp = cast(V)->getOperand(0); unsigned OldWidth = Scale.getBitWidth(); unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits(); Scale = Scale.trunc(SmallWidth); Offset = Offset.trunc(SmallWidth); Extension = isa(V) ? EK_SignExt : EK_ZeroExt; Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, DL, Depth+1); Scale = Scale.zext(OldWidth); Offset = Offset.zext(OldWidth); return Result; } Scale = 1; Offset = 0; return V; } /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it /// into a base pointer with a constant offset and a number of scaled symbolic /// offsets. /// /// The scaled symbolic offsets (represented by pairs of a Value* and a scale in /// the VarIndices vector) are Value*'s that are known to be scaled by the /// specified amount, but which may have other unrepresented high bits. As such, /// the gep cannot necessarily be reconstructed from its decomposed form. /// /// When DataLayout is around, this function is capable of analyzing everything /// that GetUnderlyingObject can look through. To be able to do that /// GetUnderlyingObject and DecomposeGEPExpression must use the same search /// depth (MaxLookupSearchDepth). /// When DataLayout not is around, it just looks through pointer casts. /// static const Value * DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, SmallVectorImpl &VarIndices, bool &MaxLookupReached, const DataLayout *DL) { // Limit recursion depth to limit compile time in crazy cases. unsigned MaxLookup = MaxLookupSearchDepth; MaxLookupReached = false; BaseOffs = 0; do { // See if this is a bitcast or GEP. const Operator *Op = dyn_cast(V); if (!Op) { // The only non-operator case we can handle are GlobalAliases. if (const GlobalAlias *GA = dyn_cast(V)) { if (!GA->mayBeOverridden()) { V = GA->getAliasee(); continue; } } return V; } if (Op->getOpcode() == Instruction::BitCast) { V = Op->getOperand(0); continue; } const GEPOperator *GEPOp = dyn_cast(Op); if (!GEPOp) { // If it's not a GEP, hand it off to SimplifyInstruction to see if it // can come up with something. This matches what GetUnderlyingObject does. if (const Instruction *I = dyn_cast(V)) // TODO: Get a DominatorTree and use it here. if (const Value *Simplified = SimplifyInstruction(const_cast(I), DL)) { V = Simplified; continue; } return V; } // Don't attempt to analyze GEPs over unsized objects. if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized()) return V; // If we are lacking DataLayout information, we can't compute the offets of // elements computed by GEPs. However, we can handle bitcast equivalent // GEPs. if (!DL) { if (!GEPOp->hasAllZeroIndices()) return V; V = GEPOp->getOperand(0); continue; } unsigned AS = GEPOp->getPointerAddressSpace(); // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices. gep_type_iterator GTI = gep_type_begin(GEPOp); for (User::const_op_iterator I = GEPOp->op_begin()+1, E = GEPOp->op_end(); I != E; ++I) { Value *Index = *I; // Compute the (potentially symbolic) offset in bytes for this index. if (StructType *STy = dyn_cast(*GTI++)) { // For a struct, add the member offset. unsigned FieldNo = cast(Index)->getZExtValue(); if (FieldNo == 0) continue; BaseOffs += DL->getStructLayout(STy)->getElementOffset(FieldNo); continue; } // For an array/pointer, add the element offset, explicitly scaled. if (ConstantInt *CIdx = dyn_cast(Index)) { if (CIdx->isZero()) continue; BaseOffs += DL->getTypeAllocSize(*GTI)*CIdx->getSExtValue(); continue; } uint64_t Scale = DL->getTypeAllocSize(*GTI); ExtensionKind Extension = EK_NotExtended; // If the integer type is smaller than the pointer size, it is implicitly // sign extended to pointer size. unsigned Width = Index->getType()->getIntegerBitWidth(); if (DL->getPointerSizeInBits(AS) > Width) Extension = EK_SignExt; // Use GetLinearExpression to decompose the index into a C1*V+C2 form. APInt IndexScale(Width, 0), IndexOffset(Width, 0); Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension, *DL, 0); // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale. // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale. BaseOffs += IndexOffset.getSExtValue()*Scale; Scale *= IndexScale.getSExtValue(); // If we already had an occurrence of this index variable, merge this // scale into it. For example, we want to handle: // A[x][x] -> x*16 + x*4 -> x*20 // This also ensures that 'x' only appears in the index list once. for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) { if (VarIndices[i].V == Index && VarIndices[i].Extension == Extension) { Scale += VarIndices[i].Scale; VarIndices.erase(VarIndices.begin()+i); break; } } // Make sure that we have a scale that makes sense for this target's // pointer size. if (unsigned ShiftBits = 64 - DL->getPointerSizeInBits(AS)) { Scale <<= ShiftBits; Scale = (int64_t)Scale >> ShiftBits; } if (Scale) { VariableGEPIndex Entry = {Index, Extension, static_cast(Scale)}; VarIndices.push_back(Entry); } } // Analyze the base pointer next. V = GEPOp->getOperand(0); } while (--MaxLookup); // If the chain of expressions is too deep, just return early. MaxLookupReached = true; return V; } //===----------------------------------------------------------------------===// // BasicAliasAnalysis Pass //===----------------------------------------------------------------------===// #ifndef NDEBUG static const Function *getParent(const Value *V) { if (const Instruction *inst = dyn_cast(V)) return inst->getParent()->getParent(); if (const Argument *arg = dyn_cast(V)) return arg->getParent(); return nullptr; } static bool notDifferentParent(const Value *O1, const Value *O2) { const Function *F1 = getParent(O1); const Function *F2 = getParent(O2); return !F1 || !F2 || F1 == F2; } #endif namespace { /// BasicAliasAnalysis - This is the primary alias analysis implementation. struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis { static char ID; // Class identification, replacement for typeinfo BasicAliasAnalysis() : ImmutablePass(ID) { initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry()); } void initializePass() override { InitializeAliasAnalysis(this); } void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired(); AU.addRequired(); } AliasResult alias(const Location &LocA, const Location &LocB) override { assert(AliasCache.empty() && "AliasCache must be cleared after use!"); assert(notDifferentParent(LocA.Ptr, LocB.Ptr) && "BasicAliasAnalysis doesn't support interprocedural queries."); AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag, LocB.Ptr, LocB.Size, LocB.TBAATag); // AliasCache rarely has more than 1 or 2 elements, always use // shrink_and_clear so it quickly returns to the inline capacity of the // SmallDenseMap if it ever grows larger. // FIXME: This should really be shrink_to_inline_capacity_and_clear(). AliasCache.shrink_and_clear(); VisitedPhiBBs.clear(); return Alias; } ModRefResult getModRefInfo(ImmutableCallSite CS, const Location &Loc) override; ModRefResult getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) override { // The AliasAnalysis base class has some smarts, lets use them. return AliasAnalysis::getModRefInfo(CS1, CS2); } /// pointsToConstantMemory - Chase pointers until we find a (constant /// global) or not. bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override; /// getModRefBehavior - Return the behavior when calling the given /// call site. ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override; /// getModRefBehavior - Return the behavior when calling the given function. /// For use when the call site is not known. ModRefBehavior getModRefBehavior(const Function *F) override; /// getAdjustedAnalysisPointer - This method is used when a pass implements /// an analysis interface through multiple inheritance. If needed, it /// should override this to adjust the this pointer as needed for the /// specified pass info. void *getAdjustedAnalysisPointer(const void *ID) override { if (ID == &AliasAnalysis::ID) return (AliasAnalysis*)this; return this; } private: // AliasCache - Track alias queries to guard against recursion. typedef std::pair LocPair; typedef SmallDenseMap AliasCacheTy; AliasCacheTy AliasCache; /// \brief Track phi nodes we have visited. When interpret "Value" pointer /// equality as value equality we need to make sure that the "Value" is not /// part of a cycle. Otherwise, two uses could come from different /// "iterations" of a cycle and see different values for the same "Value" /// pointer. /// The following example shows the problem: /// %p = phi(%alloca1, %addr2) /// %l = load %ptr /// %addr1 = gep, %alloca2, 0, %l /// %addr2 = gep %alloca2, 0, (%l + 1) /// alias(%p, %addr1) -> MayAlias ! /// store %l, ... SmallPtrSet VisitedPhiBBs; // Visited - Track instructions visited by pointsToConstantMemory. SmallPtrSet Visited; /// \brief Check whether two Values can be considered equivalent. /// /// In addition to pointer equivalence of \p V1 and \p V2 this checks /// whether they can not be part of a cycle in the value graph by looking at /// all visited phi nodes an making sure that the phis cannot reach the /// value. We have to do this because we are looking through phi nodes (That /// is we say noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB). bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2); /// \brief Dest and Src are the variable indices from two decomposed /// GetElementPtr instructions GEP1 and GEP2 which have common base /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic /// difference between the two pointers. void GetIndexDifference(SmallVectorImpl &Dest, const SmallVectorImpl &Src); // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP // instruction against another. AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, const MDNode *V1TBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo, const Value *UnderlyingV1, const Value *UnderlyingV2); // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI // instruction against another. AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize, const MDNode *PNTBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo); /// aliasSelect - Disambiguate a Select instruction against another value. AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize, const MDNode *SITBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo); AliasResult aliasCheck(const Value *V1, uint64_t V1Size, const MDNode *V1TBAATag, const Value *V2, uint64_t V2Size, const MDNode *V2TBAATag); }; } // End of anonymous namespace // Register this pass... char BasicAliasAnalysis::ID = 0; INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa", "Basic Alias Analysis (stateless AA impl)", false, true, false) INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa", "Basic Alias Analysis (stateless AA impl)", false, true, false) ImmutablePass *llvm::createBasicAliasAnalysisPass() { return new BasicAliasAnalysis(); } /// pointsToConstantMemory - Returns whether the given pointer value /// points to memory that is local to the function, with global constants being /// considered local to all functions. bool BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) { assert(Visited.empty() && "Visited must be cleared after use!"); unsigned MaxLookup = 8; SmallVector Worklist; Worklist.push_back(Loc.Ptr); do { const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL); if (!Visited.insert(V)) { Visited.clear(); return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); } // An alloca instruction defines local memory. if (OrLocal && isa(V)) continue; // A global constant counts as local memory for our purposes. if (const GlobalVariable *GV = dyn_cast(V)) { // Note: this doesn't require GV to be "ODR" because it isn't legal for a // global to be marked constant in some modules and non-constant in // others. GV may even be a declaration, not a definition. if (!GV->isConstant()) { Visited.clear(); return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); } continue; } // If both select values point to local memory, then so does the select. if (const SelectInst *SI = dyn_cast(V)) { Worklist.push_back(SI->getTrueValue()); Worklist.push_back(SI->getFalseValue()); continue; } // If all values incoming to a phi node point to local memory, then so does // the phi. if (const PHINode *PN = dyn_cast(V)) { // Don't bother inspecting phi nodes with many operands. if (PN->getNumIncomingValues() > MaxLookup) { Visited.clear(); return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); } for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) Worklist.push_back(PN->getIncomingValue(i)); continue; } // Otherwise be conservative. Visited.clear(); return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); } while (!Worklist.empty() && --MaxLookup); Visited.clear(); return Worklist.empty(); } /// getModRefBehavior - Return the behavior when calling the given call site. AliasAnalysis::ModRefBehavior BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { if (CS.doesNotAccessMemory()) // Can't do better than this. return DoesNotAccessMemory; ModRefBehavior Min = UnknownModRefBehavior; // If the callsite knows it only reads memory, don't return worse // than that. if (CS.onlyReadsMemory()) Min = OnlyReadsMemory; // The AliasAnalysis base class has some smarts, lets use them. return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min); } /// getModRefBehavior - Return the behavior when calling the given function. /// For use when the call site is not known. AliasAnalysis::ModRefBehavior BasicAliasAnalysis::getModRefBehavior(const Function *F) { // If the function declares it doesn't access memory, we can't do better. if (F->doesNotAccessMemory()) return DoesNotAccessMemory; // For intrinsics, we can check the table. if (unsigned iid = F->getIntrinsicID()) { #define GET_INTRINSIC_MODREF_BEHAVIOR #include "llvm/IR/Intrinsics.gen" #undef GET_INTRINSIC_MODREF_BEHAVIOR } ModRefBehavior Min = UnknownModRefBehavior; // If the function declares it only reads memory, go with that. if (F->onlyReadsMemory()) Min = OnlyReadsMemory; // Otherwise be conservative. return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min); } /// getModRefInfo - Check to see if the specified callsite can clobber the /// specified memory object. Since we only look at local properties of this /// function, we really can't say much about this query. We do, however, use /// simple "address taken" analysis on local objects. AliasAnalysis::ModRefResult BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) { assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) && "AliasAnalysis query involving multiple functions!"); const Value *Object = GetUnderlyingObject(Loc.Ptr, DL); // If this is a tail call and Loc.Ptr points to a stack location, we know that // the tail call cannot access or modify the local stack. // We cannot exclude byval arguments here; these belong to the caller of // the current function not to the current function, and a tail callee // may reference them. if (isa(Object)) if (const CallInst *CI = dyn_cast(CS.getInstruction())) if (CI->isTailCall()) return NoModRef; // If the pointer is to a locally allocated object that does not escape, // then the call can not mod/ref the pointer unless the call takes the pointer // as an argument, and itself doesn't capture it. if (!isa(Object) && CS.getInstruction() != Object && isNonEscapingLocalObject(Object)) { bool PassedAsArg = false; unsigned ArgNo = 0; for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); CI != CE; ++CI, ++ArgNo) { // Only look at the no-capture or byval pointer arguments. If this // pointer were passed to arguments that were neither of these, then it // couldn't be no-capture. if (!(*CI)->getType()->isPointerTy() || (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo))) continue; // If this is a no-capture pointer argument, see if we can tell that it // is impossible to alias the pointer we're checking. If not, we have to // assume that the call could touch the pointer, even though it doesn't // escape. if (!isNoAlias(Location(*CI), Location(Object))) { PassedAsArg = true; break; } } if (!PassedAsArg) return NoModRef; } const TargetLibraryInfo &TLI = getAnalysis(); ModRefResult Min = ModRef; // Finally, handle specific knowledge of intrinsics. const IntrinsicInst *II = dyn_cast(CS.getInstruction()); if (II != nullptr) switch (II->getIntrinsicID()) { default: break; case Intrinsic::memcpy: case Intrinsic::memmove: { uint64_t Len = UnknownSize; if (ConstantInt *LenCI = dyn_cast(II->getArgOperand(2))) Len = LenCI->getZExtValue(); Value *Dest = II->getArgOperand(0); Value *Src = II->getArgOperand(1); // If it can't overlap the source dest, then it doesn't modref the loc. if (isNoAlias(Location(Dest, Len), Loc)) { if (isNoAlias(Location(Src, Len), Loc)) return NoModRef; // If it can't overlap the dest, then worst case it reads the loc. Min = Ref; } else if (isNoAlias(Location(Src, Len), Loc)) { // If it can't overlap the source, then worst case it mutates the loc. Min = Mod; } break; } case Intrinsic::memset: // Since memset is 'accesses arguments' only, the AliasAnalysis base class // will handle it for the variable length case. if (ConstantInt *LenCI = dyn_cast(II->getArgOperand(2))) { uint64_t Len = LenCI->getZExtValue(); Value *Dest = II->getArgOperand(0); if (isNoAlias(Location(Dest, Len), Loc)) return NoModRef; } // We know that memset doesn't load anything. Min = Mod; break; case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: case Intrinsic::invariant_start: { uint64_t PtrSize = cast(II->getArgOperand(0))->getZExtValue(); if (isNoAlias(Location(II->getArgOperand(1), PtrSize, II->getMetadata(LLVMContext::MD_tbaa)), Loc)) return NoModRef; break; } case Intrinsic::invariant_end: { uint64_t PtrSize = cast(II->getArgOperand(1))->getZExtValue(); if (isNoAlias(Location(II->getArgOperand(2), PtrSize, II->getMetadata(LLVMContext::MD_tbaa)), Loc)) return NoModRef; break; } case Intrinsic::arm_neon_vld1: { // LLVM's vld1 and vst1 intrinsics currently only support a single // vector register. uint64_t Size = DL ? DL->getTypeStoreSize(II->getType()) : UnknownSize; if (isNoAlias(Location(II->getArgOperand(0), Size, II->getMetadata(LLVMContext::MD_tbaa)), Loc)) return NoModRef; break; } case Intrinsic::arm_neon_vst1: { uint64_t Size = DL ? DL->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize; if (isNoAlias(Location(II->getArgOperand(0), Size, II->getMetadata(LLVMContext::MD_tbaa)), Loc)) return NoModRef; break; } } // We can bound the aliasing properties of memset_pattern16 just as we can // for memcpy/memset. This is particularly important because the // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16 // whenever possible. else if (TLI.has(LibFunc::memset_pattern16) && CS.getCalledFunction() && CS.getCalledFunction()->getName() == "memset_pattern16") { const Function *MS = CS.getCalledFunction(); FunctionType *MemsetType = MS->getFunctionType(); if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 && isa(MemsetType->getParamType(0)) && isa(MemsetType->getParamType(1)) && isa(MemsetType->getParamType(2))) { uint64_t Len = UnknownSize; if (const ConstantInt *LenCI = dyn_cast(CS.getArgument(2))) Len = LenCI->getZExtValue(); const Value *Dest = CS.getArgument(0); const Value *Src = CS.getArgument(1); // If it can't overlap the source dest, then it doesn't modref the loc. if (isNoAlias(Location(Dest, Len), Loc)) { // Always reads 16 bytes of the source. if (isNoAlias(Location(Src, 16), Loc)) return NoModRef; // If it can't overlap the dest, then worst case it reads the loc. Min = Ref; // Always reads 16 bytes of the source. } else if (isNoAlias(Location(Src, 16), Loc)) { // If it can't overlap the source, then worst case it mutates the loc. Min = Mod; } } } // The AliasAnalysis base class has some smarts, lets use them. return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min); } /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction /// against another pointer. We know that V1 is a GEP, but we don't know /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, DL), /// UnderlyingV2 is the same for V2. /// AliasAnalysis::AliasResult BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, const MDNode *V1TBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo, const Value *UnderlyingV1, const Value *UnderlyingV2) { int64_t GEP1BaseOffset; bool GEP1MaxLookupReached; SmallVector GEP1VariableIndices; // If we have two gep instructions with must-alias or not-alias'ing base // pointers, figure out if the indexes to the GEP tell us anything about the // derived pointer. if (const GEPOperator *GEP2 = dyn_cast(V2)) { // Do the base pointers alias? AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, nullptr, UnderlyingV2, UnknownSize, nullptr); // Check for geps of non-aliasing underlying pointers where the offsets are // identical. if ((BaseAlias == MayAlias) && V1Size == V2Size) { // Do the base pointers alias assuming type and size. AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size, V1TBAAInfo, UnderlyingV2, V2Size, V2TBAAInfo); if (PreciseBaseAlias == NoAlias) { // See if the computed offset from the common pointer tells us about the // relation of the resulting pointer. int64_t GEP2BaseOffset; bool GEP2MaxLookupReached; SmallVector GEP2VariableIndices; const Value *GEP2BasePtr = DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, GEP2MaxLookupReached, DL); const Value *GEP1BasePtr = DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, GEP1MaxLookupReached, DL); // DecomposeGEPExpression and GetUnderlyingObject should return the // same result except when DecomposeGEPExpression has no DataLayout. if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { assert(!DL && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); return MayAlias; } // If the max search depth is reached the result is undefined if (GEP2MaxLookupReached || GEP1MaxLookupReached) return MayAlias; // Same offsets. if (GEP1BaseOffset == GEP2BaseOffset && GEP1VariableIndices == GEP2VariableIndices) return NoAlias; GEP1VariableIndices.clear(); } } // If we get a No or May, then return it immediately, no amount of analysis // will improve this situation. if (BaseAlias != MustAlias) return BaseAlias; // Otherwise, we have a MustAlias. Since the base pointers alias each other // exactly, see if the computed offset from the common pointer tells us // about the relation of the resulting pointer. const Value *GEP1BasePtr = DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, GEP1MaxLookupReached, DL); int64_t GEP2BaseOffset; bool GEP2MaxLookupReached; SmallVector GEP2VariableIndices; const Value *GEP2BasePtr = DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, GEP2MaxLookupReached, DL); // DecomposeGEPExpression and GetUnderlyingObject should return the // same result except when DecomposeGEPExpression has no DataLayout. if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { assert(!DL && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); return MayAlias; } // If the max search depth is reached the result is undefined if (GEP2MaxLookupReached || GEP1MaxLookupReached) return MayAlias; // Subtract the GEP2 pointer from the GEP1 pointer to find out their // symbolic difference. GEP1BaseOffset -= GEP2BaseOffset; GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices); } else { // Check to see if these two pointers are related by the getelementptr // instruction. If one pointer is a GEP with a non-zero index of the other // pointer, we know they cannot alias. // If both accesses are unknown size, we can't do anything useful here. if (V1Size == UnknownSize && V2Size == UnknownSize) return MayAlias; AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, nullptr, V2, V2Size, V2TBAAInfo); if (R != MustAlias) // If V2 may alias GEP base pointer, conservatively returns MayAlias. // If V2 is known not to alias GEP base pointer, then the two values // cannot alias per GEP semantics: "A pointer value formed from a // getelementptr instruction is associated with the addresses associated // with the first operand of the getelementptr". return R; const Value *GEP1BasePtr = DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, GEP1MaxLookupReached, DL); // DecomposeGEPExpression and GetUnderlyingObject should return the // same result except when DecomposeGEPExpression has no DataLayout. if (GEP1BasePtr != UnderlyingV1) { assert(!DL && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); return MayAlias; } // If the max search depth is reached the result is undefined if (GEP1MaxLookupReached) return MayAlias; } // In the two GEP Case, if there is no difference in the offsets of the // computed pointers, the resultant pointers are a must alias. This // hapens when we have two lexically identical GEP's (for example). // // In the other case, if we have getelementptr , 0, 0, 0, 0, ... and V2 // must aliases the GEP, the end result is a must alias also. if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty()) return MustAlias; // If there is a constant difference between the pointers, but the difference // is less than the size of the associated memory object, then we know // that the objects are partially overlapping. If the difference is // greater, we know they do not overlap. if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) { if (GEP1BaseOffset >= 0) { if (V2Size != UnknownSize) { if ((uint64_t)GEP1BaseOffset < V2Size) return PartialAlias; return NoAlias; } } else { // We have the situation where: // + + // | BaseOffset | // ---------------->| // |-->V1Size |-------> V2Size // GEP1 V2 // We need to know that V2Size is not unknown, otherwise we might have // stripped a gep with negative index ('gep , -1, ...). if (V1Size != UnknownSize && V2Size != UnknownSize) { if (-(uint64_t)GEP1BaseOffset < V1Size) return PartialAlias; return NoAlias; } } } // Try to distinguish something like &A[i][1] against &A[42][0]. // Grab the least significant bit set in any of the scales. if (!GEP1VariableIndices.empty()) { uint64_t Modulo = 0; for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) Modulo |= (uint64_t)GEP1VariableIndices[i].Scale; Modulo = Modulo ^ (Modulo & (Modulo - 1)); // We can compute the difference between the two addresses // mod Modulo. Check whether that difference guarantees that the // two locations do not alias. uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1); if (V1Size != UnknownSize && V2Size != UnknownSize && ModOffset >= V2Size && V1Size <= Modulo - ModOffset) return NoAlias; } // Statically, we can see that the base objects are the same, but the // pointers have dynamic offsets which we can't resolve. And none of our // little tricks above worked. // // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the // practical effect of this is protecting TBAA in the case of dynamic // indices into arrays of unions or malloc'd memory. return PartialAlias; } static AliasAnalysis::AliasResult MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) { // If the results agree, take it. if (A == B) return A; // A mix of PartialAlias and MustAlias is PartialAlias. if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) || (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias)) return AliasAnalysis::PartialAlias; // Otherwise, we don't know anything. return AliasAnalysis::MayAlias; } /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select /// instruction against another. AliasAnalysis::AliasResult BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize, const MDNode *SITBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo) { // If the values are Selects with the same condition, we can do a more precise // check: just check for aliases between the values on corresponding arms. if (const SelectInst *SI2 = dyn_cast(V2)) if (SI->getCondition() == SI2->getCondition()) { AliasResult Alias = aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo, SI2->getTrueValue(), V2Size, V2TBAAInfo); if (Alias == MayAlias) return MayAlias; AliasResult ThisAlias = aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo, SI2->getFalseValue(), V2Size, V2TBAAInfo); return MergeAliasResults(ThisAlias, Alias); } // If both arms of the Select node NoAlias or MustAlias V2, then returns // NoAlias / MustAlias. Otherwise, returns MayAlias. AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo); if (Alias == MayAlias) return MayAlias; AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo); return MergeAliasResults(ThisAlias, Alias); } // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction // against another. AliasAnalysis::AliasResult BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, const MDNode *PNTBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo) { // Track phi nodes we have visited. We use this information when we determine // value equivalence. VisitedPhiBBs.insert(PN->getParent()); // If the values are PHIs in the same block, we can do a more precise // as well as efficient check: just check for aliases between the values // on corresponding edges. if (const PHINode *PN2 = dyn_cast(V2)) if (PN2->getParent() == PN->getParent()) { LocPair Locs(Location(PN, PNSize, PNTBAAInfo), Location(V2, V2Size, V2TBAAInfo)); if (PN > V2) std::swap(Locs.first, Locs.second); // Analyse the PHIs' inputs under the assumption that the PHIs are // NoAlias. // If the PHIs are May/MustAlias there must be (recursively) an input // operand from outside the PHIs' cycle that is MayAlias/MustAlias or // there must be an operation on the PHIs within the PHIs' value cycle // that causes a MayAlias. // Pretend the phis do not alias. AliasResult Alias = NoAlias; assert(AliasCache.count(Locs) && "There must exist an entry for the phi node"); AliasResult OrigAliasResult = AliasCache[Locs]; AliasCache[Locs] = NoAlias; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { AliasResult ThisAlias = aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo, PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), V2Size, V2TBAAInfo); Alias = MergeAliasResults(ThisAlias, Alias); if (Alias == MayAlias) break; } // Reset if speculation failed. if (Alias != NoAlias) AliasCache[Locs] = OrigAliasResult; return Alias; } SmallPtrSet UniqueSrc; SmallVector V1Srcs; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { Value *PV1 = PN->getIncomingValue(i); if (isa(PV1)) // If any of the source itself is a PHI, return MayAlias conservatively // to avoid compile time explosion. The worst possible case is if both // sides are PHI nodes. In which case, this is O(m x n) time where 'm' // and 'n' are the number of PHI sources. return MayAlias; if (UniqueSrc.insert(PV1)) V1Srcs.push_back(PV1); } AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo, V1Srcs[0], PNSize, PNTBAAInfo); // Early exit if the check of the first PHI source against V2 is MayAlias. // Other results are not possible. if (Alias == MayAlias) return MayAlias; // If all sources of the PHI node NoAlias or MustAlias V2, then returns // NoAlias / MustAlias. Otherwise, returns MayAlias. for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { Value *V = V1Srcs[i]; AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo, V, PNSize, PNTBAAInfo); Alias = MergeAliasResults(ThisAlias, Alias); if (Alias == MayAlias) break; } return Alias; } // aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases, // such as array references. // AliasAnalysis::AliasResult BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, const MDNode *V1TBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo) { // If either of the memory references is empty, it doesn't matter what the // pointer values are. if (V1Size == 0 || V2Size == 0) return NoAlias; // Strip off any casts if they exist. V1 = V1->stripPointerCasts(); V2 = V2->stripPointerCasts(); // Are we checking for alias of the same value? // Because we look 'through' phi nodes we could look at "Value" pointers from // different iterations. We must therefore make sure that this is not the // case. The function isValueEqualInPotentialCycles ensures that this cannot // happen by looking at the visited phi nodes and making sure they cannot // reach the value. if (isValueEqualInPotentialCycles(V1, V2)) return MustAlias; if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy()) return NoAlias; // Scalars cannot alias each other // Figure out what objects these things are pointing to if we can. const Value *O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth); const Value *O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth); // Null values in the default address space don't point to any object, so they // don't alias any other pointer. if (const ConstantPointerNull *CPN = dyn_cast(O1)) if (CPN->getType()->getAddressSpace() == 0) return NoAlias; if (const ConstantPointerNull *CPN = dyn_cast(O2)) if (CPN->getType()->getAddressSpace() == 0) return NoAlias; if (O1 != O2) { // If V1/V2 point to two different objects we know that we have no alias. if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) return NoAlias; // Constant pointers can't alias with non-const isIdentifiedObject objects. if ((isa(O1) && isIdentifiedObject(O2) && !isa(O2)) || (isa(O2) && isIdentifiedObject(O1) && !isa(O1))) return NoAlias; // Function arguments can't alias with things that are known to be // unambigously identified at the function level. if ((isa(O1) && isIdentifiedFunctionLocal(O2)) || (isa(O2) && isIdentifiedFunctionLocal(O1))) return NoAlias; // Most objects can't alias null. if ((isa(O2) && isKnownNonNull(O1)) || (isa(O1) && isKnownNonNull(O2))) return NoAlias; // If one pointer is the result of a call/invoke or load and the other is a // non-escaping local object within the same function, then we know the // object couldn't escape to a point where the call could return it. // // Note that if the pointers are in different functions, there are a // variety of complications. A call with a nocapture argument may still // temporary store the nocapture argument's value in a temporary memory // location if that memory location doesn't escape. Or it may pass a // nocapture value to other functions as long as they don't capture it. if (isEscapeSource(O1) && isNonEscapingLocalObject(O2)) return NoAlias; if (isEscapeSource(O2) && isNonEscapingLocalObject(O1)) return NoAlias; } // If the size of one access is larger than the entire object on the other // side, then we know such behavior is undefined and can assume no alias. if (DL) if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *DL, *TLI)) || (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *DL, *TLI))) return NoAlias; // Check the cache before climbing up use-def chains. This also terminates // otherwise infinitely recursive queries. LocPair Locs(Location(V1, V1Size, V1TBAAInfo), Location(V2, V2Size, V2TBAAInfo)); if (V1 > V2) std::swap(Locs.first, Locs.second); std::pair Pair = AliasCache.insert(std::make_pair(Locs, MayAlias)); if (!Pair.second) return Pair.first->second; // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the // GEP can't simplify, we don't even look at the PHI cases. if (!isa(V1) && isa(V2)) { std::swap(V1, V2); std::swap(V1Size, V2Size); std::swap(O1, O2); std::swap(V1TBAAInfo, V2TBAAInfo); } if (const GEPOperator *GV1 = dyn_cast(V1)) { AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2); if (Result != MayAlias) return AliasCache[Locs] = Result; } if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); std::swap(V1TBAAInfo, V2TBAAInfo); } if (const PHINode *PN = dyn_cast(V1)) { AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo); if (Result != MayAlias) return AliasCache[Locs] = Result; } if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); std::swap(V1TBAAInfo, V2TBAAInfo); } if (const SelectInst *S1 = dyn_cast(V1)) { AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo); if (Result != MayAlias) return AliasCache[Locs] = Result; } // If both pointers are pointing into the same object and one of them // accesses is accessing the entire object, then the accesses must // overlap in some way. if (DL && O1 == O2) if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *DL, *TLI)) || (V2Size != UnknownSize && isObjectSize(O2, V2Size, *DL, *TLI))) return AliasCache[Locs] = PartialAlias; AliasResult Result = AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo), Location(V2, V2Size, V2TBAAInfo)); return AliasCache[Locs] = Result; } bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V, const Value *V2) { if (V != V2) return false; const Instruction *Inst = dyn_cast(V); if (!Inst) return true; if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck) return false; // Use dominance or loop info if available. DominatorTreeWrapperPass *DTWP = getAnalysisIfAvailable(); DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr; LoopInfo *LI = getAnalysisIfAvailable(); // Make sure that the visited phis cannot reach the Value. This ensures that // the Values cannot come from different iterations of a potential cycle the // phi nodes could be involved in. for (SmallPtrSet::iterator PI = VisitedPhiBBs.begin(), PE = VisitedPhiBBs.end(); PI != PE; ++PI) if (isPotentiallyReachable((*PI)->begin(), Inst, DT, LI)) return false; return true; } /// GetIndexDifference - Dest and Src are the variable indices from two /// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic /// difference between the two pointers. void BasicAliasAnalysis::GetIndexDifference( SmallVectorImpl &Dest, const SmallVectorImpl &Src) { if (Src.empty()) return; for (unsigned i = 0, e = Src.size(); i != e; ++i) { const Value *V = Src[i].V; ExtensionKind Extension = Src[i].Extension; int64_t Scale = Src[i].Scale; // Find V in Dest. This is N^2, but pointer indices almost never have more // than a few variable indexes. for (unsigned j = 0, e = Dest.size(); j != e; ++j) { if (!isValueEqualInPotentialCycles(Dest[j].V, V) || Dest[j].Extension != Extension) continue; // If we found it, subtract off Scale V's from the entry in Dest. If it // goes to zero, remove the entry. if (Dest[j].Scale != Scale) Dest[j].Scale -= Scale; else Dest.erase(Dest.begin() + j); Scale = 0; break; } // If we didn't consume this entry, add it to the end of the Dest list. if (Scale) { VariableGEPIndex Entry = { V, Extension, -Scale }; Dest.push_back(Entry); } } }